As a conventional technology of this type, there is one disclosed in Patent Document 1. In this Patent Document 1, amount structure for a control valve unit on a construction machine such as a hydraulic excavator is disclosed. According to this conventional technology, a unitary assembly is fabricated beforehand by mounting the control valve unit on a bracket and connecting hydraulic pipes at one ends thereof to the control valve unit. The bracket included in the unitary assembly is fixed on a swing frame by bolts to mount the control valve unit on an upper structure